This invention relates to transilluminators for transilluminating electrophoresis gels with ultraviolet light.
A common method for separating, identifying or purifying DNA from a mixed sample is by electrophoresis of the sample through an agarose gel. The electrophoretic migration rate of DNA through agarose gel is dependent upon the molecular weight of the DNA, as well as such considerations as the agarose concentration and the strength of the electric field. The electrophoresis technique is simple and rapid, and results in the formation of distinct bands of DNA within the gel.
After electrophoresis for a sufficient period, electrophoresis gels are typically stained to visualize the bands of DNA, often with low concentrations of the fluorescent dye ethidium bromide. Ethidium bromide which becomes bound-up, or intercalated, between bases of the DNA has an increased fluorescent yield, as compared to free ethidium bromide in solution. Ultraviolet (UV) radiation is absorbed by bound ethidium bromide dye and re-emitted in the red-orange region of the visible spectrum. Thus, the location and relative amount of DNA is detectable by examination of an ethidium bromide-stained electrophoresis gel under illumination by UV light.
One apparatus used to illuminate electrophoresis gels produces UV light in a closed box. A light source within the box transmits UV light through a horizontal window provided in the top of the box. A typical light source is a plurality of parallel fluorescent lamps. The window is typically made of purple filter glass. This filter glass blocks all light except that within a narrow range centered around the specific UV region which creates the above-mentioned fluorescence in the ethidium bromide bound to the DNA. A gel is positioned over the window for illumination by the UV light, which will pass through the window below and illuminate the gel. Such an apparatus is referred to as a transilluminator.
In many applications, the DNA bands within the gel will be further compared and evaluated based on the distance travelled and upon the relative intensity of the fluorescence between bands. These determinations will in turn be somewhat dependent upon the relative strength of the background UV light intensity. The differences in fluorescence of different DNA bands of a given sample, or between a sample and background fluorescence or the fluorescence of trace DNA contaminants can be complicated by the transilluminator's own fluctuations in UV light intensity across the window. For this reason, it is desirable that an even background of UV light be provided for the gel.